A new MOSFET-C universal filter structure for VLSI

Abstract
A continuous-time all-MOS universal filter structure is proposed. The structure is based on the MOSFET-C design approach. It achieves complete MOS nonlinearity cancellation and does not require the use of fully balanced op-amps. General topological requirements are established that are necessary for the conversion of active-RC prototypes to MOSFET-C counterparts, such that MOS nonlinearity cancellation is achieved. Accordingly, a universal active-RC prototype filter structure, which meets the necessary requirements, is presented and its MOSFET-C version is developed. Nonideal effects that may degrade the performance at high frequency are discussed and ways for improvement are proposed. Results obtained from a test chip have verified the viability of the proposed structures. The chip is an implementation of a MOSFET-C universal filter in a 3.5- mu m CMOS process. The filter is successfully tuned over a wide range of pole frequencies (0 to 100 kHz) using op-amps with a measured gain bandwidth of only 1.2 MHz.

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